1. Field of the Invention
The present invention relates to the field of image recognition and, more particularly, to a method for locating face landmarks of an image by using dynamic programming.
2. Description of Related Art
Conventionally, local features are widely utilized for recognition in order to find a location of the face appearing in an image. As known that local features of the face comprise eyes, nose, lips, cheeks, forehead, etc. One or more of such local features of the image are compared with fetched image in order to confirm whether they are the same. As such, an exact representation of each local feature of the face is essential to a successful subsequent recognition of a portion in an image (e.g., the face).
Typically, there are two approaches for finding face landmarks (e.g., eyes, nose, and lips) from an image of the face. The first one is to use image processing, such as filtering, morphological operation, or threshold operation, to select a number of candidate portions from the face landmarks, and then confirm a portion or all of the candidates as features. The second one employs a graph matching method to represent a face model by a featured graph, wherein nodes are used to represent feature locations, and edges between the nodes are used to represent relative locations of the features. The feature value of each node is obtained by performing the image processing. The model is then shifted around the image, so as to locate the face landmarks by image matching.
An image processing method is disclosed in U.S. Pat. No. 5,805,475 which first calculates a threshold by a heuristic method or statistics. The threshold is critical to a successful recognition. In the patent, each of the morphological or threshold operation involves a number of threshold determinations. In the case of utilizing the heuristic method, the threshold is required to be amended in response to variability of images as observed. As a result, the implementation is difficult and an efficient recognition of face landmarks in the image is made impossible.
A graph matching method is disclosed in U.S. Pat. No. 6,222,939 which describes a number of nodes each having a feature value. For comparing with a graph model, it is required to calculate feature values of an image. Although not all pixels are required to calculate, a great number of node locations are required to fetch. In this patent, a two dimensional searching on the image is essential. Also, the feature values for describing the face image are obtained by a complex two-dimensional calculation. Thus, a number of complex calculations and comparisons are required in each process of face landmarks location of an image. This bears a great burden upon the computer system, resulting in a significant decrease of efficiency.
Therefore, it is desirable to provide a novel method for locating face landmarks in an image to mitigate and/or obviate the aforementioned problems.